The present invention relates to a swing rotor of a centrifugal separator which is widely used in medical, pharmaceutical, and genetic engineering and in other various fields.
More specifically, the present invention relates to improvement of strength and performance of the swing rotor of a centrifugal separator.
Furthermore, the present invention relates to energy saving, structural simplification, and cost reduction for centrifugal separators.
The swing rotors generally used in the field of clinical medicine for separating blood specimens sampled for the purpose of various inspections need to cover the maximum rotational speeds ranging from 2,000 min−1 to 20,000 min−1. This kind of conventional swing rotors are disclosed, for example, in the unexamined Japanese patent publication No. 49-15066, Japanese utility model No. 63-2110, Japanese utility model No. 63-35797, and the unexamined Japanese patent publication No. 6-285390.
FIGS. 7 to 9 show an example of this type of conventional swing rotors.
In FIGS. 7 to 9, a rotor body 1 has a central hole 1a. A drive shaft (not shown) of a motor (not shown) is coupled into the central hole 1a to rotate the rotor body 1. The rotor body 1 chiefly consists of symmetrically branched arms 2 extending in radial directions at equal angular intervals (90°) for holding a total of four buckets 4 between respective arms 2. Hinge pins 3 are attached to distal ends of respective arms 2. Each bucket 4 is supported by two hinge pins 3 which extend coaxially from opposed arms 2. Each bucket 4 is thus swingable about an axis defined by these coaxial hinge pins 3. The bucket 4 accommodates a centrifugal tube rack 6. A plurality of centrifugal tubes 5, each storing a sample solution to be tested or inspected, are positioned in a predetermined pattern in this rack 6.
The rotor body 1 is made of a stainless steel or an aluminum alloy and is manufactured by the forging, casting, machining or the like. Each pin 3 is integrally formed with the rotor body 1 from the same material. Alternatively, each pin 3 is a separate part independent of the rotor body 1. For example, the pin 3 can be manufactured by the machining from a stainless steel or a comparable steel. Then, the pin 3 is installed or inserted into an engaging hole formed at a predetermined portion of the arm 2. The bucket 4 is made of an aluminum alloy and manufactured by the machining or casting. Alternatively, the bucket 4 can be manufactured by the press working from a stainless steel sheet.
The assurance term or guaranteed lifetime as well as the allowable rotational speeds of each swing rotor are determined by a manufacturer of this rotor. Users can use this rotor safely as far as they obey the restrictions and conditions determined by the manufacturer. If the swing rotor is forcibly used at higher speeds exceeding the allowable upper limit, or if the swing rotor is continuously used for a long time exceeding the guaranteed lifetime, the swing rotor will break and a centrifugal separator will be damaged. The energy caused when the swing rotor breaks is so large that the centrifugal separator shifts or moves suddenly and closely toward an operator of this machine and endangers the operator.
From the above, all of the parts constituting a swing rotor need to guarantee the performance of this swing rotor and also need to assure satisfactory mechanical strength for the guaranteed operation speeds and lifetime.
On the other hand, recent centrifugal separators are required to perform advanced centrifugal separations at higher speeds and under large centrifugal forces and also required to process a large number of samples to be tested or inspected at a time.
The buckets used for the conventional swing rotors, when manufactured by the machining from a metallic material, generally require a large amount of labor time and man power in the process of cutting or machining the metallic material into the shape of a bucket. This increases the manufacturing cost. Furthermore, the metallic bucket has a large specific gravity and a large thickness due to inherent nature of metallic material. When a centrifugal force is applied on the bucket, a rotor body receives a large centrifugal load. This will possibly deteriorate the performance of a centrifugal separator.
On the other hand, the buckets for the conventional swing rotors, when manufactured by the press working from a stainless steel, generally require expensive pressing dies as well as specialized pressing machine facilities. This increases the manufacturing cost. Furthermore, when a stainless steel is subjected to the press working, there is the possibility that a manufactured bucket has uneven portions having different thicknesses. For example, to assemble the stainless-made bucket with a swing rotor, very complicated or difficult processing is required to form appropriate coupling or engaging portions on this bucket. This processing will possibly leave weak portions having insufficient thicknesses on the processed bucket. As a result, the manufactured bucket will have a poor strength and may break during a severe centrifugal operation.
Furthermore, when equipped with metallic buckets, a swing rotor is subjected to a large inertia moment due to a large specific gravity of the metallic buckets. This requires a drive motor to generate a large driving power. Furthermore, a long time will be necessary for the drive motor to accelerate and decelerate the rotor. The rotational energy of a swing rotor increases in proportion to increased moment of inertia. Considering this rotational energy, a centrifugal separator needs to be equipped with a protective barrier (i.e., a safety wall or partition) having a sufficient strength capable of protecting an operator against breakage of a swing rotor.